In communications networks, there is always a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, time-division duplex (TDD) operation is supported by the mobile communication standard Long Term Evolution (LTE). In TDD the uplink (UL) and downlink (DL) share the same carrier frequency. This has an advantage compared to frequency-division duplex (FDD), using different carriers for UL and DL, in the terms that only one carrier is needed for the communication. Furthermore, TDD is, in theory, rather flexible since the UL/DL sub frame allocation could be adapted based on current traffic need.
In practical TDD deployments, the possibility to use different UL/DL sub frame allocation in different cells are rather limited, both for cells using the same carrier frequency and for cells using adjacent carrier frequencies. This is mainly due to large dynamics in the communications network, where the received signal power level could be, for example, around −100 dBm, while the transmitted signal power level could be, for example, above 20 dBm, i.e., a dynamic range of 120 dB.
Therefore, if one wireless terminal transmits with higher power at the same time as another wireless terminal receives a signal with lower power while being located in close vicinity of each other, there may be (up to) 100 dB or larger interference levels than signal level. Assuming ideal transceivers it would be possible to deploy different UL/DL allocations on adjacent TDD carriers, but due to real-world imperfections, including non-linear elements, there will be transmission (TX) leakage which means that the transmitted signal also interferes with the transmissions in the adjacent channels. A TX leakage ratio in the range of 30-40 dB may be acceptable. The ratio is defined as the ratio between total interference power seen at the adjacent carrier due to transmission in the desired carrier and the transmission power at the desired carrier. The resulting leakage power generally depends on the frequency location of the interfering system and the victim system. Thus closely spaced systems interfere each other in a more challenging way than two systems placed further apart in frequency.
One way to handle such issues, according to the state of the art, is to have coordination between the network (NW) nodes (such as between the radio base stations). However there are several issues associated therewith. The NW nodes may not be operatively connected; for instance even if coordination between NW nodes is possible, there may not be any information about the relative location of the wireless terminals. Hence denying extra UL slots only due to that one active wireless terminal is present in an adjacent NW node may be too restrictive. Moreover, the interfering and victim system may be operated by different operators, thus any communications between the NW nodes may not be possible.
Hence, there is still a need for an improved configuration of wireless terminals.